The present invention is directed to an explosive charge operated fastening element setting device with a guidance tube containing a driving piston axially displaceably mounted within a housing. An outlet tube axially guided in the housing is displaceable co-axially with the guidance tube. The outlet tube extends from the housing and partially overlaps the guidance tube within the housing. A U-shaped spring clip is positioned in the outlet tube with legs extending through grooves in the tube with the grooves located diametrically opposite one another and extending transversely of the firing direction of the device. The legs are arranged in axial alignment with shoulders extending radially from the forward end of the guidance tube.
An explosive powder charge operated fastening element setting device is disclosed in a Hilti prospectus at page 4.78 In this device, after driving a fastening element, a guidance tube for the driving piston is displaced in a housing in the firing direction for returning the piston into the firing position. The displacement of the guidance tube is effected by moving an outlet tube in the firing direction with the outlet tube coupled to the guidance tube so that it is displaceable to a limited extent. A U-shaped spring clip supported in the outlet tube serves as the coupling member and it has legs extending through grooves into the bore of the outlet tube and the legs co-act with protuberances on the guidance tube located at its forward end. The spring clip legs are formed of strip-shaped spring steel, and are regained in position due to their elastic or flexural properties.
When the outlet tube is moved in the firing direction, the forward sides of the legs directed in the firing direction abut in a blow-like manner against the protuberances on the guidance tube. As a result, high specific compressive loads are developed which lead to the deformation of the spring clip and of the protuberances, impairing the function and useful life of these parts. An additional disadvantage is that the gas pressures developed during the firing operation in the device act radially outwardly on the legs and, after a relatively brief period of operation, reduce the spring action so that the legs can no longer fulfill the coupling action in a reliable manner.